The radial truck tire industry in this country predominantly utilizes precured tread material to cover the buffed area of the casing with a cushion layer of uncured rubber between them.
Curing systems for such rebuilt tires require that either the entire tire or the outer surface thereof be enveloped before being subjected to a curing medium in a suitable temperature range and at an appropriate pressure. Pressures within the curing chamber force the tread material against the cushion layer and the casing but, due to the tread design, pressure is distributed unequally resulting in the migration of the softened cushion layer to areas of lower pressure. Such migrations cause a distorted tread and in some areas, reduced strength. A further disadvantage to the use of envelopes is that they have an insulating effect which slows the build-up of heat within it.
It has been proposed, see U.S. Pat. No. 3,136,673 to R. J. Carver, to provide a cushion layer consisting of two parts, one layer on the buffed area of the casing and the other on the underside of the precured tread material. When the two layers were brought together, cross-linking occurred at ambient temperatures. With a steel belt locked about the entire tread and the tire inflated, the assembly was placed in a warm environment to speed the cross-linking. The difficulty with this procedure was that the cured cushion was weak. In addition, the procedure, if used with radial casings, would require appropriately crowned steel bands.
In U.S. Pat. No. 3,925,129 to J. D. Blankenship, a tire retreading system employed non stretchable bands encircling the margins of the tread surface of the precured tread material after the rebuilt tire had been stitched. In order that the tensioned bands would function to maintain seals between the casing and the tread material, the tires were provided with inner tubes and mounted on rims and the band tensions increased either by inflating the tire against the resistance of the bands or by temporarily reducing the outside diameter of the tire before placing the bands in position and then allowing the tire to return towards its original size against the bands. One of the short comings of this system is that inner tubes are required in retreading bias tires with high enough inflation pressures to insure that the tires, which have a natural tendency to become elastic in the hot curing medium, maintain their diameters, or want to grow slightly lest the seals be lost at the interfaces. Another short coming is that radial tires with their girdling belts under the treads, are for practical purposes, dimensionally stable to both temperature and inflation pressure changes and therefore cannot be inflated to tension the bands nor their diameter reduced by spreading the beads to allow band tensioning as with the bias weave tires.
In accordance with U.S. Pat. No. 4,098,936 to V. Rawls, the precured tread material was formed with gutter-like grooves marginally of the tread surface. After a tire was rebuilt and stitched, a retaining wire was wrapped tightly around each groove to hold the tread in place during curing. Retainers which could be expanded before being placed in the grooves as well as those that would contract to tighten them were also discussed.
In my copending application Ser. No. 161031, filed Feb. 26, 1988, interfaces are protected against being penetrated by curing media by extruding uncured rubber, curable at temperatures above 200.degree. F., over the margins of the casing and the tread material to form blending layers.